Neuralgia possesses no "pathology," if by that word we intend to signify the knowledge of definite anatomical changes always associated with the disease, in a manner that we can exhibit or exactly describe. It also possesses no demonstrable causes, if we employ the word "causes" in the old metaphysical sense. And yet I am very far from admitting, what seems to be so generally taken for granted, that we know less about the seat, the nature, and the conditions of neuralgia than of other diseases. On the contrary, I believe, with all deference to the supporters of the ordinary opinion, that we know more about neuralgia, in all these respects, than we do about pneumonia, only our knowledge is not of the superficial and obvious kind, but requires the aid of reason and reflection to develop and turn it to account. It has long been a matter of surprise to me, that even able writers have been content to talk about this disease (as, indeed, they have been content to speak of many nervous diseases) with an inexplicable looseness of phraseology. They speak of its "protean" forms; whereas, in my humble judgment, its forms are by no means specially numerous. They insist on the mysterious and unintelligible manner of its outbreaks, remissions and departure; but I shall try to show that, although, in the investigation of neuralgia, we are continually stopped in particular lines of inquiry by what seems to be ultimate facts, susceptible of no further immediate solution, the channels of information open to us are so unusually numerous as to enable us to accumulate a mass of information which, upon further reflection, will be found to furnish the materials of a synthesis of the disease singularly clear and effective for every practical purpose of the physician. In one important particular I especially hope to convince the reader that a large proportion of the mystification as to the pathology of neuralgia is gratuitous, and the result of great carelessness in estimating the comparative value of different facts. I hope to show clearly that, as regards both the seat of what must be the essential part of the morbid process, and the general nature of the process itself, we possess very definite information indeed. I expect, in short, to convince most readers that the essential seat of every true neuralgia is the posterior root of the spinal nerve in which the pain is felt, and that the essential condition of the tissue of that nerve-root is atrophy, which is usually non-inflammatory in origin. This doctrine seems, at first sight, presumptuous,[16] in the confessed absence or extreme scarcity of dissections which even bear at all upon the question. But one source of the extraordinary interest which the pathology of neuralgia has long possessed for me resides in this very fact, that I am convinced we can demonstrate the above apparently difficult theorem by means of pathological observations on the living